How Does ABS Systems Work?

The antilock brake system or the ABS control unit helps to maintain control and directional stability of an automobile in case of extreme braking circumstances. This is achieved by controlling the rotational speed of every wheel by metering the brake line pressure at the time of extreme braking. The system works on most types of road surfaces and decreases the risk of an accident and severity of an impact. Research has shown that an antilock brake system can decrease the chance of a vehicle accident by 18%. ABS brake systems were introduced in the late seventies and have enjoyed great technological advances since that time.
Not only does ABS provide non-skid functionality but it also supports electronic stability control, brake assist, traction control, etc. Recently, additional sensors have been added to the system, gyroscopic sensors and steering wheel angle sensors. Both synchronize to match the direction of the car with the direction of the steering wheel. The wheel angle sensor also helps the ABS system control the outer wheels to have a more positive braking effect when compared to the inner wheels on the curve.
An anti-lock brakes system (ABS) is an important tool to help drivers slow down when they need to stop quickly on a slippery surface. Anti-lock brake systems work every winter to help prevent many car accidents from occurring. Most new cars now automatically come with ABS as a standard safety feature. Though anti-lock brakes do not completely prevent all car accidents, they do contribute to the overall safety of vehicles on slippery surfaces.
ABS systems contain a controller that functions as a computer. Controllers measure speed and control the valves and pump of the ABS system. If the controller senses a difference in wheel speed in the speed sensors, the ABS overrides your pressure on the brake pedal. This complicated process begins with detection at your computer and speed sensors. The computer evaluates the speed of the slipping wheel and controls the valves to provide a measured response. The controller evaluates wheel speed and rotation as well as continuity between the wheels.
The ABS assembly is made up of a central electronic unit, four solenoid valves and two or more electric hydraulic pumps. The function of the electric hydraulic pump is to supply brake fluid pressure to the braking system by forcing hydraulic pressure to a reservoir located in the accumulator. The four solenoid pressure valves control brake fluid pressure for each individual wheel. During an ABS operation event, one or more of the solenoid valves dump brake line pressure to a particular wheel allowing it to start turning.
Based on this evaluation, the controller decides whether the car can regain control without ABS, if the system requires complete takeover to return control to the car, or if the valve should release pressure to return the brake system to normal. The controller performs this assessment within seconds.
Valves control the amount of fluid available to the lines and brake system. Once the controller tells the valves of the ABS that the system needs to control the skid, this engages a pump on the ABS. The pump releases and applies variable pressure to the braking system to stop the car or regain traction. The pumping system also varies the application of the brakes at a rate to control the skid.
If multiple wheels lose control, the controller sends different messages to each wheel based on its assessment of stopping requirements. ABS varies the rate of brake application based on information collected from the wheel sensors. ABS automatically applies the brakes based on each individual wheel evaluation to reestablish control.
ABS pumps your brakes at a much greater speed that humanly possible. This feels like a pulsing in the brake pedal when ABS is engaged. Some ABS systems can apply brakes up to 30 to 40 times per second, much faster than humanly possible.
Activating your ABS system temporarily prevents the initiation of regular braking. As soon as the ABS system gains traction, the controller notifies the valves to release pressure from the brake lines. This restores the normal braking system to the vehicle. The pump restores normal pressure to the brake lines after application of the ABS.
Squealing brakes is an indication of a problem with the brake system. Most of the time a squealing noise can be a warning that the brake pads are worn down and need to be replaced. Other causes can be overheated brake pads or rotors. Sometimes rust can get impregnated on the brake lining material and cause grumbling or squeaking noises. When cleaning brake components prior to service precautions must be taken. Most brake systems contain microscopic fibers that are extremely hazardous to your health. While cleaning with brake system cleaner there is an increased chance of inhaling these fibers that accumulate on the brake components. Cleaning should be done in a well ventilated area, use an air filter respirator if possible for best results.
When the ABS system detects a problem a fault code is stored in the ABS system control unit. When an error occurs the ABS warning light located on the dashboard flashes or stays on steadily. The ABS computer stores a diagnostic code until the malfunction has been repaired. To retrieve ABS trouble codes on older vehicles can be tricky because of the variation of retrieval methods; in this case a car repair manual is needed. On newer vehicles a diagnostic information connector is located under the dash on the driver's side; a trouble code scanner can be attached to retrieve ABS codes similar to engine trouble codes.


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